Biological Processes in the Soil and Floodwater - The Biogeochemistry of Submerged Soils - page 158

Table 5.5 Invertebrates in ricefield soil and floodwater

Densities ( number m − 2 )

Comments

Min. Max. Mean

Microcrustacea
Ostracods 0 98 000 6000 Stimulated by factors that

increase primary production,
such as N and P fertilizer.

Filter bacteria and algae
from water

Copepods 0 40 000 33 000

Cladocerans 0 33 000 900

Insect larvae
Chironomids 0 10 000 600 Feed on epipelic algae at soil

surface and on floating algae

Mosquitoes 0 7000 170

Molluscs
Snails 0 1000 200 Inhibited by high acidity, N

fertilizer and pesticides;
stimulated by high organic
matter. Graze on epipelic
and floating algae, and on
algae epiphytic on plant
stems

Oligochaetes
Tubificids 0 40 000 10 000 Stimulated by factors that

increase primary production
and bacterial decomposers;
inhibited by high soil bulk
density

Source : Roger (1996), Simpson et al . (1993a, 1994a,b).

organic matter and applications of N fertilizer, presumably through the effects of
these on primary production and bacterial decomposers on which oligochaetes
feed. Populations of insect larvae and molluscs are successional over the season
following the cycles of algal populations. But no general trends have been estab-
lished for the dynamics of oligochaetes, though this may reflect the paucity of
data (Roger, 1996).
The effects of macrofauna on the soil biogeochemistry can be summarized
(Aller, 1994):

• manipulation of particles: exposure of substrate resulting in increased decom-
position;

• grazing: consumption of microbes, stimulation of microbial growth, increased

mineralization;

• excretion of substrate and nutrients: stimulation of microbial growth, increased

mineralization;